The transition of the Type II to the Type I pneumocyte after lung injury and during the normal developmental process is accompained by considerable change in cell shape and function. The Type I alveolar-lining cells are extremely thin and cover 96% of the alveolar surface. We hypothesize that during this differentiation process, the cytoskeletal and structural proteins must undergo change in isoform and organization, accompanying this change in shape and function. We will focus on the keratin intermediate filament proteins which are markers for virtually all epithelial cells. The specific isoforms of keratin present are characteristic of the differentiation state of the epithelial cell. We propose to use individual specific monoclonal antikeratin antibodies to determine the keratin species present in Type II and Type I alveolar epithelial cells: 1) in normal rat lung; 2) after exposure to 85% or 100% oxygen or intratracheal instillation of bleomycin sulfate (these 2 models of lung injury may have different effects on Type II cell differentiation); 3) during normal development. Sections of lung will be treated with these antibodies by immunoperoxidase techniques at the light and electron microscope levels. We will also prepare antibodies against other cytoskeletal proteins (actin(s), collagen(s)) to detect change in isoform or organization by similar techniques. We will also study the transition of Type II pneumocytes in culture. The culture condition provides a model for the in vivo transition of the Type II to the Type I pneumocyte as, in culture, the Type II cells spread out, lose the ability to produce surfactant and exhibit decreased numbers of lamellar bodies. We will analyze Type II cells in culture on various substrates (plastic, laminin, fibronectin, polyHEMA) by 2-dimensional gel electrophoresis on cytoskeletal and aqueous-soluble fractions of cell extracts to determine how change in cell shape affects the expression of cytoskeletal and other proteins and what effect substrata have on the differentiation process. These experiments will answer important questions about the role of cytoskeletel proteins as Type II pneumocytes are induced to differentiate and alter their shape and function after lung injury and during development.